Electric induction furnace



Aug. 1, 1933. K. SCHMIDT ELECTRIC INDUCTION FURNACE Filed Oct. 25. 1929Patented Aug. 1, 1933 UNITED STATES ELECTRIC INDUCTION FURNACETempelhof, Germany Application October 25,

1929, Serial No. 402,526,

and in Germany October 25, 1928 2 Claims.

Application has been filed in Germany October This application relatesto electric furnaces and more particularly to an improved form ofinduction furnace. having a circular closed'core.

Heretofore it has been the practice to use induction furnaces eitheroperating with high frequency current in the absence of iron parts, orlow frequency current furnaces having a surrounding iron core usuallywith an air gap in which the crucible is located. The first type has theadvantage' that it permits the heating of any form of material, but onthe other hand it is not economical due to considerable inductiveleakage. Further drawbacks to low frequency furnaces employing cruciblesnow in use are that they require annular or ring-shaped crucibles, thecore is so situated that the heat from the crucible comes into contacttherewith, causing it to bend, and the difiiculty of removing thecrucibles.

The principal object of this invention is to provide a furnace having alaminated core so positioned that the lines of magneto-motive force actperpendicularly to the axis of the working chamber.

A further object is to provide a furnace from which the crucible or workmay be removed with ease and which is economical to operate, due to thereduction of bending of the core. A clearer conception of theconstruction, operation and further objects of the invention may be hadfrom thefollowing specification taken in conjunction with theaccompanying drawing in which:

Figure 1 is a View of the invention. in cross section.

Figure 2 is a top view of Figure 1, and

Figure 3 is a perspective view of the core showing the method of windingthe coil on the core.

The furnace comprises a crucible i surrounded by a laminated sheet metalcore 2 formed of circular plates having holes 3 therein, in each ofwhich a portion of the winding may be positioned. The heating chamberformed by the core is filled as far as possible by the material orcrucible to be heated and the heat rising therefrom does not come incontact with the core. The whole construction is exceedingly compact andof high stability. The crucible proper or material to be heated may bewithdrawn vertically by means of a crane or hoist, thereby reducing thepossibility'of spilling which often occurs when the crucible iswithdrawn horizontally, as has formerly been the practice and which hasthereby necessitated the use of a car or other device. It

is also apparent that, if desired, the crucible may be permanently builtinto the core and the entire structure tipped to permit drawing themelt.

The use of a cylindrical core prevents the heat which rises out of thecrucible from damaging the core and thereby greatly reduces bendingeffects and, as set forth above, facilitates removal of the crucible.The inductive winding of the core may be distributed in a manner similarto that used in a three phase alternating current generator as is shownin Figure 3. The windings consist of three wires 5, 6 and 7 which arepositioned as shown. one wire in each aperture 3.

In Figs. 1 and 2 the windings are shown as insulated copper tubes 4.,with only one tube in each hole 3. The insulation is mica or othermaterial of low thermal conductivity. The tubular. form of the windingprovides a ready means for cooling the winding as well as thesurrounding magnetic material of the core. The cooling medium may beeither airor Water passing through the tubular windings. Where a solidconductor, as in Fig. 3, is employed cooling channels may be provided inthe magnetic core. By positioning the windings in the hole 3 parallelwith the vertical axis of the furnace, the magnetcmotive force isconcentrated at the vertical axis.

The frequency of the alternating currents used may vary within widelimits and thus normal frequencies from the line as well as lower orhigher frequencies may be used. The latter course naturally requires avery careful insulation of the iron sheets employed. Multiphase currentsmay also be employed and, as is known, they will produce a rotatingfield which, as with multiphase generators or motors, will create arotary action on the material to be fused, so that a considerable motionis imparted to the molten metal. By changing the amplitude of thephases, by reversing the windings or by changing the angle of the phase,the rotating field can be infiu enced in any desired manner, or'it maybe altogether eliminated. Consequently, the-movement of the metal can beregulated in any desired way without the necessity of materiallyreducing the heat generated, or of cooling the metal by the introductionof agitating apparatus.

The use of a multi-phase system renders possible the connection of sucha furnace to a normal three phase line, a property which is of thegreatest importance in the interest of a uniform loading of the threephases of the network. A furnace according to this invention may also beused to advantage for glowing, tempering and so on,

by removing the crucible and directly substituting the work to beheated. A special advantage in connection with all the purposesmentioned is .that the whole furnace may be constructed of continuoussheets of metal in contradistinction to the known low frequencyfurnaces, so that a solid furnace body is obtained, which can easily behandled, and which is also economical to oper- I ate.

What is claimed is:

1. An electric induction furnace comprising a laminated ring of magneticmaterial having openings therethrough near the inner periphery andparallel to the axis of the ring, heating means for reducing metal to amolten state and for causing its rotation consisting of a single set ofmultiphase windings arranged in said openings, and a removable cruciblepositioned within and surrounded by the ring of magnetic material and 1having an unobstructed interior.

2. An electric induction furnace comprising a crucible having anunobstructed interior and pro- 1

